The present invention relates to a fuel cell system and a gas leak determination method for the fuel cell system, and more particularly to an improved technique for determining a gas leak in a fuel gas supply system in a short period of time and with a high level of precision.
A fuel cell system which is capable of directly extracting chemical energy generated by an oxidation reduction reaction between a fuel gas and an oxidizing gas as electric energy is used as a power generation system in a fuel cell vehicle. In this type of fuel cell system, various shutoff valves (for example, a high-pressure hydrogen tank valve, a hydrogen supply valve, an FC stack inlet valve, an FC stack outlet valve, a purge valve, and so on) are disposed in a fuel gas supply passage for supplying fuel gas from a hydrogen supply source to a fuel cell. As a method of diagnosing a defect in these various shutoff valves, Japanese Unexamined Patent Application Publication 2000-274311, for example, proposes a technique for determining a valve defect in which a shutoff valve disposed in a fuel gas supply passage of a vehicle is closed to create a closed space in the fuel gas supply passage, and a valve defect is determined when a pressure decrease rate relative to the elapse of time in the closed space falls below a pressure decrease rate threshold. However, the pressure decrease speed on the downstream side of the shutoff valve varies according to the operating conditions of the vehicle, or in other words the fuel consumption rate. Hence, when the fuel consumption rate falls in accordance with the operating conditions of the vehicle, a large amount of time is required for the pressure to decrease on the downstream side of the shutoff valve, and therefore a defect cannot be diagnosed speedily. In consideration of this background art, Japanese Unexamined Patent Application Publication 2003-308868 proposes a technique for reducing the pressure on the downstream side of a shutoff valve within a short time period when diagnosing a defect in the shutoff valve by increasing the consumed power of a power consumption section (a motor or the like) to increase the fuel consumption amount of the fuel cell.